Abstract [Objective] To analyze the related factors of C5 nerve root palsy after Open-door cervical expansive laminoplasty in patients with cervical myelopathy and investigate the clinical features and possible pathogenesis of postoperative C5 nerve root palsy. [Methods] From January 2008 to January 2014，153 patients with multilevel cervical spondylotic myelopathy treated by open-door cervical expansive laminoplasty were reviewed at the authors, institution. There were 98 males and 55 females with a mean age of 58.9 years. The patients suffered with postoperative C5 palsy were observed. The correlation among the pre- and post-operative cervical curvature, preoperative change of EMG and the incidence of C5 palsy were analyzed. [Results] The different incidence of C5 palsy between abnormal EMG group and normal EMG group was statistically significant（P<0.05）. The preoperative cervical curvature was of significant difference between the palsy and non-palsy groups(P<0.05), but the postoperative cervical curvature was of no significant difference(P=0.051). the pre- and post-operative JOA improvement rate was of significant difference between the palsy and non-palsy groups(P<0.05). [Conclusion] The larger curvature of cervical and abnormal EMG were the risk factors of C5 palsy. JOA improvement rate in the non-palsy group was higher than that in the palsy group.